1. Field of the Invention
The present invention relates to a silicon carbide semiconductor device, and more particularly to a silicon carbide semiconductor device having a termination region.
2. Description of the Background Art
In recent years, in order to achieve a high breakdown voltage and low loss of semiconductor devices such as a MOSFET (Metal Oxide Semiconductor Field Effect Transistor), use thereof in a high temperature environment, and the like, silicon carbide has been adopted as a material for semiconductor devices. Silicon carbide is a wide band gap semiconductor having a band gap larger than that of silicon, which has been conventionally widely used as a material for semiconductor devices. Hence, by adopting silicon carbide as a material for a semiconductor device, the semiconductor device can have a high breakdown voltage, reduced ON resistance, and the like. Further, the semiconductor device adopting silicon carbide as its material has an advantage that its characteristics are less likely to be deteriorated when it is used in the high temperature environment, when compared with a semiconductor device adopting silicon as its material.
For example, Japanese Patent Laying-Open No. 2003-101039 describes a high breakdown voltage silicon carbide semiconductor device including a plurality of guard rings provided concentrically, and a region provided inside an innermost guard ring portion and having an impurity concentration higher than that in the innermost guard ring portion. Further, Japanese Patent Laying-Open No. 2008-270412 discloses a silicon carbide SBD (Schottky Barrier Diode) including a plurality of p type guard ring portions provided on an outer peripheral side of a p type RESURF portion.
In addition, “Semiconductor SiC Technology and Applications, the Second Edition” by Hiroyuki Matsunami, et al., Nikkan Kogyo Shimbun, Ltd., Sep. 20, 2011, pp. 352 to 353 describes a silicon carbide SBD having a JTE (Junction Termination Extension) region configured to alleviate electric field strength by forming a p type layer with a concentration low enough to be depleted. The above document describes that a breakdown voltage is improved by forming guard ring portions having impurity concentrations which become lower toward the outside.
In order to increase the breakdown voltage of a silicon carbide semiconductor device, it is necessary to widen a termination region of the silicon carbide semiconductor device. However, if the termination region of the silicon carbide semiconductor device is simply widened, an element region of the silicon carbide semiconductor device is narrowed.